WASHINGTON, May 19 (Reuters) - A popular diet that eliminates wheat and milk protein does not appear to help children with autism, but early behavioral treatments do, researchers reported on Wednesday.

The findings are sure to disappoint many parents who have been trying to manage autism, which affects as many as 1 in 100 U.S. children.

"It would have been wonderful for children with autism and their families if we found that the gluten-free, casein-free diet could really help, but this small study didn't show significant benefits," said Dr. Susan Hyman of the University of Rochester in New York, who led the study.

Gluten is the protein found in wheat, rye and other grains, while casein is a milk protein.

"The removal of gluten and casein from the diet of a controlled group of young children with autism, all of whom were screened for celiac disease ... did not demonstrate a change in sleep habits, bowel habits, activity or core symptoms of autism," Hyman said.

Autism includes a range of conditions, from the social awkwardness seen in Asperger's syndrome to profound and severe disabilities. There is no cure and little information about treatments that work.

Hyman's team studied the diet after seeing Internet reports from parents who believed they saw effects in their children. There is some evidence linking autism with some potential abnormality or activity in the intestines and theories suggest proteins absorbed in the bowels may affect autism symptoms.

They tested 14 children aged 2 to 5, making sure they did not eat gluten or casein.

INTENSE STUDY

After at least four weeks on the strict diet, the children were randomly given snacks containing either gluten, casein, both or placebo in randomized order. The snacks were disguised so neither the child nor the caregiver knew they contained a "hidden" ingredient.

Parents, teachers and a research assistant filled out standardized surveys about each child's behavior the day before they received the snack, two hours after and 24 hours later, and the parents kept a diary throughout the experiment about eating, sleep and bowel habits.

The children were videotaped to assess social interaction.

There were no differences after the challenge, the researchers told the International Meeting for Autism Research in Philadelphia.

Hyman said other diets may work. "We only eliminated food containing gluten and casein," she said.

While on the special diet, the children took part in early childhood education programs, and those seemed to help their symptoms, Hyman said.

"All got the same early education care," Hyman said. "Early childhood education appears to work in helping symptoms of autism."

She also said it is possible that children with lactose intolerance or celiac disease -- an allergy to wheat protein -- may be helped by the diet.

"This is really just the tip of the iceberg. There are many possible effects of diet, including over- and under-nutrition, on behavior in children with autism spectrum disorders that need to be scientifically investigated so families can make informed decisions about the therapies they choose for their children," Hyman said.